A serious cat disease

Feline Infectious Peritonitis (FIP)

What is FIP?

Nervous CatFeline infectious peritonitis (FIP) is a serious disease in cats caused by a mutation of the common feline enteric (gut) coronavirus (FeCoV). The mutation allows the otherwise insignificant virus to enter to escape the gastrointestinal tract lining by entering the gut macrophage cells (an immune system cell) and hitching a ride to other parts of the body, infecting the abdominal cavity, chest cavity, eyes and in some instances, the brain. Usually a cat’s immune system prevents clinical FIP but in some cats infected with enteric FeCoV, the immune system fails to eliminate the infection and clinical FIP develops with devastating consequences. FIP itself is not contagious to other cats and the feline coronavirus is not the same as the human coronavirus that causes COVID-19.

Clinical signs of FIP

Cats with clinical FIP develop a range of clinical signs such as:

  • Fever unresponsive to antibiotics
  • Fluid in the abdominal and/or chest cavities
  • Palpable enlarged abdominal lymph nodes
  • Change in the symmetry of the pupils or eye colour
  • Neurological signs (brain infection)

The clinical signs depend on whether the cat has the effusive or ‘wet’ form of FIP or non-effusive or ‘dry’ form of FIP, although more often than not, there is a combination of wet and dry forms present, known as a ‘mixed wet and dry’ FIP.

Cats at risk of FIP
The majority of cats that develop FIP affected are young between 3 months and 2 years of age, or elderly cats, and the disease often affects purebred cats (especially Ragdolls) or cats that have been housed together in a rescue facility where multiple cats share a litter tray. Any cat that has previously been exposed to enteric feline coronavirus can potentially develop FIP, but in the vast majority of cats, the enteric coronavirus is insignificant and does not require any treatment.
Diagnosis of FIP

Laboratory changes on blood work typical of FIP may include:
– Hyperglobulinaemia (elevated globulins)
– Non-regenerative anaemia (low red blood cell count)
– Neutrophilic leukocytosis (elevated white blood cell count)
– Elevated liver parameters (ALT, ALP, elevated bilirubin)

An albumin to globulin ratio of < 0.45 raises the suspicion of FIP in a young cat. It’s important to note that no single laboratory abnormality will occur 100% of the time. Fluid analysis for cases of ‘wet’ FIP typical changes include: – Specific gravity of 1.017-1.047 – Protein > 35g/L
– Low cellularity with non-degenerate neutrophils and macrophages

For a definitive diagnosis of FIP the following tests can be used:
– Immunofluorescence (IFA) for FIP antigen or FIP PCR on fluid sample (‘wet’ FIP)
– Immunohistochemistry or immunocytochemistry from an FNA or biopsy sample from an enlarged lymph node (‘wet’ or ‘dry’ forms)
– Brain MRI and/or CSF tap (‘dry’ FIP)

Co-morbidities such as toxoplasmosis and/or mycoplasmosis (if anaemic) could be present, so ruling out these diseases via toxoplasma titres (IgG and IgM) and a Mycoplasma PCR test is helpful. Testing for FIV and FeLV is recommended.

False negatives are common, so if a definitive diagnosis of FIP cannot be obtained, or the owner has financial constraints, then a remdesivir treatment trial can be considered. Usually, FIP cats respond rapidly to remdesivir, with fever resolving and significant improvement noticed within 3-5 days of starting treatment, sometimes as early as 24 hours after the first injection.

Dr Gretta Howard's interest in FIP

As a new graduate vet in the year 2000, Dr Gretta had to deliver very sad news to a young family with their beautiful new kitten who had developed FIP. The kitten had a very swollen abdomen full of fluid, a high fever and breathing problems. Unfortunately, at this time, there was no treatment available and as the cat was suffering, euthanasia was the only option.

18 years later, Dr Gretta first heard about GS-441524, a new anti-viral FIP treatment, when she attended a lecture about its discovery at an Australian and New Zealand College of Veterinary Scientists conference in Queensland in 2018.

Dr Gretta has always had an interest in infectious diseases and as a side-project during the first COVID-19 Sydney lockdown, Dr Gretta started volunteering as a veterinarian with the FIP Warriors Facebook group and via email, communicating with vets and owners located all over the world, including USA, Europe, Russia, South America, Middle East, Asia and home in Australia, to assist remotely in the management of their FIP cases. Through this rewarding, yet challenging experience, Gretta has collaborated with many other veterinarians and cat rescue groups who treat vast numbers of FIP cases.

Remdesivir and FIP

Remdesivir (Veklury, Gilead Sciences) was approved in 2020 as an anti-viral for use in COVID-19 patients. Remdesivir is actually the prodrug for GS-441524, but unfortunately, Gilead was not interested in pursuing the feline market for this drug.

In 2020, BOVA Animal Compounding Pharmacy secured a supply of remdesivir, which means that vets can write a script to acquire it for their patients. If the pharmacy supplies the medication via a veterinary script, it is not the vet supplying the drug. This avoids cat owners attempting to illegally import an unlabelled, unregistered drug and deal with the consequences if caught by the authorities. Prior to remdesivir being available to veterinarians, this was the only option for clients who wished to treat their FIP positive cats, and as it is illegal for vets to import unregistered medications, owners were left to source medication and learn how to inject their cats themselves without veterinary guidance.

Dr Gretta Howard’s friend and colleague, one of the world’s most well-known and respected feline specialistsDr Richard Malik, has been instrumental in volunteering his time and expertise helping vets treat sick cats world-wide and in conjunction with other FIP researchers, has put together a FIP remdesivir treatment protocol for veterinarians. This gives vets a much better way to effectively treat FIP patients while they remain under their care and is therefore a much better overall outcome for the welfare of cats with this horrible disease, which was previously a death sentence.

Treatment protocol for FIP cats with remdesivir

Dr Gretta Howard co-authored an article in The Veterinarian: “Treatment of FIP in cats with remdesivir” with Dr Richard Malik and Dr David Hughes, which discusses the protocol for FIP treatment with remdesivir.

As this is still in experimental stages, the treatment protocol in this article will be subject to change over time, so it is important to obtain the most current recommendations that have been based on research findings.

Remdesivir veterinary prescription to BOVA Animal Compounding Pharmacy

In NSW, while it is acceptable to charge a script fee, it is illegal for vets to place a mark-up on compounded medication from pharmacies. At Turramurra Veterinary Hospital, the script is emailed (and then the hard-copy posted) to BOVA then once received, clients can make a direct payment to BOVA for the medication, which is then delivered to the vet hospital within 24-48 hours. Scripts for remdesivir are marked URGENT for remdesivir for priority post. It is recommended for critical cases, that the script is email and paid for prior to 3pm so that vials can be posted to the vet clinic on the same day.

Remdesivir dose recommendations for FIP treatment

Dose recommendations continue to evolve over time as further research is pursued and more cases are treated with remdesivir.

Dose recommendations (updated July 2021):

Effusive ‘wet’ FIP                    9mg/kg once daily by subcutaneous injection

Non-effusive ‘dry’ FIP             15mg/kg once daily by subcutaneous injection

Ocular FIP                                12mg/kg once daily by subcutaneous injection

If patients are critically ill, then an intravenous protocol can be used for the first 3 days using an initial dose of 10mg/kg once daily while the cat is hospitalised on intravenous fluids. It is critical to monitor these cases closely for pleural effusion (fluid in the chest).

Generally, we recommend continuing treatment for 12 weeks (84 days) then stop if the cat is doing clinically well and the blood results look promising. An increase in dose and/or extension of the course of treatment may be recommended based on the clinical response to therapy, blood parameters or signs of relapse.

The cost of treatment is expensive, and it is important to note that many cats with FIP have been cured at much lower doses, such as 5-6mg/kg once daily by subcutaneous injection, so if clients cannot afford the higher doses, a lower dose for a shorter duration is better than no dose.

Mefloquine orally in FIP treatment

In addition to remdesivir, mefloquine (Larium) can be used orally at a dose rate of 10-12mg/kg orally twice a week. For an average sized cat, this is approximately ¼ x 250mg tablet. Dr Gretta recommends starting this once the cat is stable on remdesivir therapy, then continuing to use mefloquine 3 months beyond stopping remdesivir therapy. There is some evidence to suggest that this protocol reduces the chance of a relapse.


Monitoring is recommended every 4 weeks until the end of the 12-week treatment period, however, if the cat is doing well on remdesivir therapy, and the owner has financial constraints, then less frequent reassessments may be recommended. Monitoring recommendations vary from patient to patient.

A steady improvement in the albumin to globulin ratio is one of the markers to look for when determining response to therapy. The only problem with this approach, is that we rarely have a pre-FIP albumin to globulin ratio to compare to, so we never really know what a specific individual’s normal levels are. It’s vital to treat the patient and not just the laboratory values, because there is no one marker that determines whether a patient is cured.

Treating veterinarians must use their best judgement based on clinical response to treatment, laboratory values and the owner’s financial constraints to make decisions about dose increases and extensions and when to discontinue treatment.

Pet health insurance cover

If your cat was healthy at the time of taking out pet insurance cover, then your insurance company may cover the cost for FIP treatment. Approval is on a case-by-case basis and subject to review. If you have pet insurance cover for your cat but your claim has been declined, then ask your vet to phone the insurance company’s vet help line to have the claim reviewed. This has sometimes resulted in an overturn on a decision to deny a claim, resulting in a client being able to claim the costs for FIP treatment.

Many drugs used in veterinary medicine, including remdesivir, are not APVMA approved, but are approved by the Australian Register of Therapeutic Goods (ARTG). Given research and journal articles supporting remdesivir as a proven FIP treatment, if your vet prescribes remdesivir for FIP treatment, then it is recommended to submit an insurance claim for consultations and treatment costs.

FIP face-to-face or telehealth consultations with Dr Gretta Howard

Dr Gretta Howard is available for face-to-face (pending COVID restrictions) or telehealth consultations for cat owners based in NSW who wish to seek her opinion on FIP case management. In addition to a consultation, this involves reviewing any prior veterinary records, laboratory results and management recommendations. Consultations (face-to-face or telehealth) are $159 and subsequent reassessment is $99, payable over the phone at the time of booking your appointment. 

If you would like to go ahead with a consultation, please phone our customer care team on (02) 9988-0198 so they can book you in with Dr Gretta Howard at a suitable time. Please ensure to include an update on whether your cat is critically ill or stable (eating, comfortable) so that priority can be given to very sick cats. 

Once booked in, please forward your previous veterinary records, laboratory results and a summary of your own via email to our reception team, including your cat’s current weight. Where possible, these records can be reviewed prior to the appointment time. 

Unfortunately, due to veterinary board regulations, Dr Gretta is unable to provide consultations outside of NSW but may be able to provide you with the names of vets comfortable treating FIP in your Australian state so that you can arrange an appointment with them. Your vet is welcome to email their questions to Dr Gretta Howard for further assistance on FIP case management if required.

Further resources

Below are some further resources that you or your vet can access to assist with FIP treatment, which was previously a fatal diagnosis in cats. Being able to provide some treatment options that can be life-saving for an owner of a cat that has been diagnosed with FIP is a huge step forward in managing this terrible disease.

Please click on the following links to reference the PDF article or website.


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